A few users who have upgraded to OS X Mountain Lion are noticing what appears to be a bug involving sound processing on their systems. When the problem occurs, the Mac's audio output will begin to stutter and the mouse cursor will pause and jump. At times the system may become unresponsive when the stuttering happens, but usually continues working again after a moment or two.
The cause of the problem is not clear at the moment, as it seems to come and go unpredictably, and also happens in a number of different software and hardware setups. While some have thought external audio interfaces or the use of specific software packages might be contributing to this problem, there is no consistency to these claims. In some cases where people have multiple audio interfaces it happens for all devices, but for others only one of the interfaces is affected.
When this problem happens, affected users have reported noticing a jump in the system's core audio processing service (coreaudiod) over its normal sub-10 percent CPU usage when observing it in Apple's Activity Monitor utility.
Affected users, assuming the problem stems from a specific configuration of theirs, have tried performing numerous general troubleshooting steps such as clearing caches, fixing permissions, resetting PRAM, creating new user accounts, and even formatting and reinstalling OS X; however, in most cases the problem persists. For some who have Apple's latest MacBook Air and MacBook Pro, a fix may be present in the latest SMC firmware updates that Apple made available for proper compatibility with Mountain Lion's Power Nap feature, but for others there so far is no such update.
Unfortunately, if you are experiencing this problem, there is little you can do to manage it for now. If your system does not show the stuttering on at least one of several attached audio interfaces, you can try using the Sound system preferences to switch to the working one as your default audio input and output device.
Hopefully Apple will address this problem soon, as it not only results in unpleasant sounds but also can lock up affected systems for a few minutes, and do so regularly enough to impede work. If you have just upgraded to Mountain Lion and are experiencing this problem to a degree that you cannot use your system without regular hangs and audio stuttering, then for now your best bet would be to reinstall OS X Lion or restore from a backup.
This issue is reminiscent of another recent audio-related problem, in which many new MacBook Air systems have been showing progressive audio degradation when used with Apple's Thunderbolt Display. Apple has just issued its first update for OS X Mountain Lion to developers for testing, so hopefully this will contain a fix for both of these audio-related issues.